Formation of coating on copper containing materials

ABSTRACT

A METHOD OF INDUSTRIALLY FORMING VERDIGRIS ON A SURFACE OF AN ARTICLE OF COPPER OR AN ALLOY THEREOF WITHIN A SHORT PERIOD, WHICH RESEMBLES THAT NATURALLY FORMED, SO AS TO PREVENT THE SURFACE FROM CORROSION AND TO GIVE A DECORATIVE AND ARTISTIC APPEARANCE, BY TREATING SUCH A SURFACE WITH A SOLUTION CONTAINING AMMONIUM SULPHATE AND MERCURIC CHLORIDE OR FURTHER TREATING WITH AN ETHYL NITRATE SOLUTION.

United States Patent 3,669,766 FORMATION OF COATING ON COPPER CONTAININGMATERIALS Mitsunosuke Fukawa, 20-21, l-chome, Matsugaoka, Kugenuma,Fujisawa-shi, Kanagawa-ken, Japan; and Haruo Oishi, 21-7, S-chome,Nakano-ku; Kicllitaro Saruya, 7-14, Z-chome, NIinami-cho, Tanashi-shi;and Akira Nagai, 17, Z-chome, Fukuro-machi, Kita-ku, all of Tokyo,Japan; and Yoshitaro Nagai, 13-3, l-chome, Nishikamata, Ota-ku, Japan NoDrawing. Filed Nov. 28, 1969, Ser. No. 880,929 Int. Cl. C23f 7/00 US.Cl. 148-624 1 Claim ABSTRACT OF THE DISCLOSURE A method of industriallyforming verdigris on a surface of an article of copper or an alloythereof within a short period, which resembles that naturally formed, soas to prevent the surface from corrosion and to give a decorative andartistic appearance, by treating such a surface with a solutioncontaining ammonium sulphate and mercuric chloride or further treatingwith an ethyl nitrate solution.

BACKGROUND OF THE INVENTION It is well known that in the atmosphereoxygen, steam carbonic acid gas, sulphides, and the like act on copperand copper alloys to form basic copper salts which constitute verdigrishaving an elegant colour tone. However, recently in cities and town, itis impossible to expect the formation of a beautiful film of verdigrisnaturally due to the fact that a clean copper surface is blackened.Under these circumstances, an artificial formation of verdigris isrequired. Meantime, many methods have been well known for formingverdigris artificially on the industrial art works by employingchemicals. In one of these methods copper salts and ammonium chlorideare used.

The copper salts are dissolved in water or an acid material is providedfor replenishing copper ion which constitutes the formation ofverdigris. The ammonium chloride or a substitute thereof reacts withcopper to produce blue copper hydroxide. In addition, alum, arsenousacid, and the like are added to accelerate the reaction of the copperion and improving the durability of the verdigris.

However, even if it is possible to treat small numbers of the industrialart works or the like by the prior art, it is substantially impossibleto treat large areas such as those of roofs and walls of a religious,monumental building, or the like by the conventional method.

SUMMARY OF THE INVENTION This invention relates to chemical methods offorming verdigris on a surface of an article of copper or an alloy ofwhich the main constituent is copper, which is of industrialapplication.

The object of this invention is to provide a method of forming verdigriswhich resembles that naturally formed, on a surface of an article ofcopper or an alloy of which the main constituent is copper, so as toform a film of verdigris within a short period which is effective forpreventing the surface from undesirable deterioration such as corrosionand giving the surface a decorative and artistic appearance.

The invention provides a process of forming verdigris on the surface ofan article which comprises either copper or an alloy of which the mainconstituent is copper, comprising bringing the surface into contact witha solution containing ammonium sulphate and mercuric chloride. Thesolution preferably contains copper sulphate. Preferably the pH of thesolution is from 4 to 5 and the concentration of ammonium sulphate isabove 25 grams per litre.

By virtue of this invention, the drawbacks inherent to the conventionalmethod are removed or mitigated and the formation of verdigris may becarried out industrially and mass-productively in response to theabove-mentioned requirement.

:In the process of the invention an amalgam of copper and mercury isformed from the main constituent and the solution of the invention sothat the substance of the verdigris film is produced by combining coppersulphate and others within a short period to convert a film into theverdigris film which resembles that naturally formed. The verdigris filmformed as above may subsequently be treated with a solution containingan alkyl (particularly ethyl) nitrite so as to convert the film intoanother verdigris film having a colour tone which is nearer to that ofthe naturally formed verdigris without aging, and a stability.

DESORIPT ION OF THE PREFERRED EMBODIMENTS In accordance with the presentinvention, an A liquor is used, which comprises such constituents as 50to 150 g. of ammonium sulphate, 2 to 8 g. of cupric sulphate, and 5 to15 g. of mercuric chloride, dissolved in one litre of water, of which pHvalue is adjusted in the range from 4.0 to 5.0 by adding 28 percentaqueous solution ammonia thereto. A C liquor may also be used, whichcomprises one litre of water containing such solutes as 5 to 20 g. ofammonium chloride, 20 to 60 g. of sodium chloride, and 50 to g. ofcopper nitrate mixed with 30! to 100 cc. of 15 percent alcoholic ethylnitrite solution.

In operation, a cleaned surface of a copper article is sprayed with orimmersed in the A liquor and allowed to stand in the atmosphere todryness. The dried surface is again treated as above. A film ofverdigris having a more bluish colour tone than that of naturally formedverdigris is formed, which becomes more to resemble to the latter byaging. In order to obtain an artificial verdigris more resembling thenatural one just after the treatment, the article may be sprayed with orimmersed in a C liquor in a similar manner as the treatment with the Aliquor. 1

Now the treatment in accordance with this invention will be explainedfrom the chemical point of view. The cleaned surface of copper or analloy thereof reacts with the A liquor as follows:

Volts CuCu ++2e 0.34 HgHg ++2e 0.86

Copper (amalgamated copper) and ammonium sulphate in the A liquor reactwith atmospheric oxygen as follows, yielding ammonia:

A part of the ammonium is expelled into the atmosphere in the gaseousstate and another part reacts with copper sulphate as follows, yieldingcupric hydroxide and regenerating ammonium sulphate.

CuSO +2NH OH-Cu(OH) +(NH4) SO (3) The cupric hydroxide combines withcopper sulphate on the instant of formation thereof, yielding basiccopper sulphate which forms the substance of the blue verdigris.

The ammonium sulphate is one of the essential ingredients to the Aliquor. The use of ammonium sulphate of the concentration below 50 g./l.cannot provide the blue verdigris of the desired thickness because ofthe insufiicient yield of ammonia and, hence, cupric hydroxide. Thus,below 50 g./l. there is no substantial eifect of the ammonium sulphateconcentration, but the use of a com centration higher than 150 g./l. isnot necessary.

It is clear that the reaction in accordance with the Formula 2 requiresoxygen. Therefore, not only the mode of contact of the article to betreated with the A liquor is important, but also the drying conditionfor the treated article is essential. In view of our experiments, it ispreferred to naturally dry for a period of 15 to 20' minutes conditionalon that the humidity is 50 to 60% and the temperature is 15 to 30 C.

The reaction for forming verdigris is greatly affected by theconcentration of mercuric chloride in the A liquor. Even in the absenceof Hg, the reaction as the Formula 1 would arise. But in such acondition as above, the reaction velocity would be slow, and a littlequantity of ammonium would be produced so as to form a little verdigris.The mercuric chloride can be used in a concentration range from 5 g./l.to 15 g./l. to ensure the formation of sufiicient amounts of the amalgamand cupric hydroxide; however, no significant effect is obtained with aconcentration of higher than 15 g./l. of mercuric chloride. The amalgamof copper separated on the surface thereof is likely to serve as abonding material for the verdigris film. By virtue of the amalgam, theverdigris film becomes well adhesive. It is sufiicient that the A liquorhas copper sulphate in concentration of 0.5 to 2 g./litre as Cu. In mostcases, a concentration of l g./litre Cu is appropriate. Of course,copper sulphate is an indispensable constituent for the treatment.However, too much copper sulphate would result a too thick film whichwould be apt to peel. On the contrary, too little copper sulphate wouldform too little subject of verdigris so that it is impossible to form averdigris film having a desired thickness and a desired colour tone. Theammonium sulphate in the A liquor is also an indispensable constituent.In the absence of this constituent, verdigris is not formed. It is notnecessary to define the concentration of ammonium sulphate in the Aliquor appreciably strictly. However, it is necessary to contain atleast 25 g. thereof in one litre of the A liquor.

The A liquor may be used at the normal temperature, and the pH valuethereof suitable for the process is between 4.0 and 5.0. The amount offormation of verdigris becomes less as the pH value rises. The amount offormation and quality of verdigris become extremely bad at a pH valuehigher than 7.0 and as the pH value decreases below 4.0, there are theadditional bad effect of poor adhesion of verdigris to the substrate.The verdigris film may be formed by giving attention to the conditionsas above.

The action and effect of the C liquor are as follows. When a film formedby the action of the A liquor is sprayed with the C liquor, ethylnitrite contained in the C liquor acts as a reductant, so that basiccopper sulphate in the film and copper nitrate in the C liquor areconverted into basic copper nitrite and the cupric ion is reduced to thecuprous ion so asto form a basis cuprous salt which constitutesyellowish green verdigris. It is necessary that the C liquor contains atleast g. of ethyl nitrite as C H ONO per one litre thereof, while theallowable upper limit of the concentration of ethyl nitrite isindefinite.

The ammonium chloride and sodium chloride in the C liquor serve as asource of chlorine ion by means of which the color of verdigris ischanged from bluish green to yellowish green. This change of color doesnot occur in the absence of chlorine ion, even if the ethyl nitrite ispresent in the system. The concentration of ammonium chloride to be usedmay be 5-20 g./l., but it is not so critical. The sodium chloride havingthe color-changing function mentioned above should be used at aconcentration from 20 g./l. to 60 g./l. The concentration below 20 g./l.cannot impart sufiicient color-changing function to the C liquor. Thecopper nitrate is suitably used at a concentration of from 50 g./l. to100 g./l. The use of copper nitrate in excess of 100 g./l. results inthe formation of too thick a film of verdigris which is liable to peeloff, and less than 50 g./l. affects the deepness of the color.

By virtue of the C liquor, the colour tone of the verdi-,.

gris is converted and the adhesion to the base metal is improved.

Examples of the process of the invention will now be given.

were dissolved in water which was then diluted to one litre and adjustedto a pH from 4.0 to 5.0 by 28 percent ammonia solution.

A cleaned surface of copper was sprayed with 200 to 500 cc./m. of the Aliquor composed as above at normal temperature and allowed to drynaturally.

The condition for drying in this case is very important. It is mostpreferable that the natural drying requires a period of about 15 to 20minutes at a temperature of from 15 to 30 C., and a humidity of from 50to 60%. Stagnant excess liquid formed by the spraying operation willresult in a verdigris film inferior in adhesion, if left as it is on thesheet. Accordingly, it is necessary to suck away such stagnant excessliquid by a sucking means.

The film formed was sprayed with the A liquor repeatedly three times.

Except in the initial operation, the spraying and drying operation donot require such strict conditions.

Example 2 A liquor: G. Ammonium sulphate (NH SO 50 Copper sulphate CuSO-5H O 5 Mercuric chloride HgCl 8 were dissolved in water which was thendiluted to one litre and adjusted to a pH from 4.0 to 5.0 by 28 percentammonia solution.

C liquor: G. Ammonium chloride NH.,C1 15 Sodium chloride NaCl 50 Coppernitrate Cu(NO -3H O 100 The three constituents were dissolved in waterwhich was then diluted to one litre, and then 100 cc. of 15 percentalcoholic ethyl nitrate solution were added. Asurface of copper plate,cleaned by means of liquid honing, was sprayed with the A liquor atnormal temperature at the rate of from 200 to 500 cc. per square meter.Stagnant excess liquid was sucked away. The plate was naturally driedfor 10 to 30 minutes at a humidity from 50 to percent and a temperaturefrom 5 to 35 C.

The, film yielded by treating with the A liquor was sprayed with Cliquor at a normal temperature at the rate of to 200 cc. per squaremeter and naturally dried. The length of the drying period does notsubstantially aifect to the formation of the verdigris. The treatmentwith the C liquor was repeated once more and the again sprayed plate wasnaturally dried. It is not necessary to wash the treated plate withwater, but it is rather preferred to allow it to stand as it is for aperiod of two or three days.

What is claimed is:

1. A method of producing on the surface of an article having copper asthe main constituent, a large scale yellowish green verdigris, whichcomprises the steps of:

(a) treating the surface of the article with an aqueous solutioncomprising 50 to 150 grams per liter ammonium sulfate, 5 to 15 grams perliter mercuric chloride and 2 to 8 grams per liter copper sulfate, thepH of which is adjusted to 4.0 to 5.0; and

(b) treating the verdigris thus formed with an aqueous 10 solutioncomprising 50 to 100 grams per liter copper nitrate, 10 grams per literor more of ethyl nitrite in a 15% alcoholic solution, and a chlorine iondonor of 5 to 60 grams per liter.

References Cited UNITED STATES PATENTS 1,951,304 3/1934 Freeman et al1486.24 3,473,970 10/1969 Robey 1486.24 X

OTHER REFERENCES Hopkins, Scientific American Cyclopedia of Formulas,Scientific Am. Pub. Co., 1925, p. 441.

RALPH S. KENDALL, Primary Examiner US. Cl. X.R. 148-6. 14

